Aerodynamic Investigations of Low-Aspect-Ratio Thin Plate Wings at Low Reynolds Numbers

2012 ◽  
Vol 28 (1) ◽  
pp. 77-89 ◽  
Author(s):  
Y.-C. Liu ◽  
F.-B. Hsiao
Keyword(s):  
Aspect Ratio ◽  
Thin Plate ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Flow Structures ◽  
Low Aspect Ratio ◽  
Aerodynamic Properties ◽  
Stall Angle

ABSTRACTTo realize the relationship between flow structures of wingtip vortices and post stall characteristics of low aspect-ratio wings, this paper experimentally studies the aerodynamic characteristics and the corresponding flow structures of the rectangular thin-plate wings at Reynolds numbers between 104 and 105. The aerodynamic properties to be studied include lift, drag, slopes at linear and nonlinear range of the lift curves and lift-to-drag ratios of the tested wings with the aspect ratio varying from 1.0 to 3.0. The flow structures regarding the leading-edge separation vortices and wingtip vortices at upper surface and near-wake regions of the wings are also investigated by smoke-wire visualization. Results indicate that the high stall angle of attack and vortex lift are clearly manifested to induce the nonlinear increase in the lift curves as the aspect ratio reaches less than 1.6. This phenomenon is specifically observed to augment the aerodynamic properties with the decrease of the aspect ratio. Additionally, the corresponding flow visualization also indicates that the wingtip vortices and the areas of highly affected regions are duly increased with the increase of the angle of attack up to 40°, which makes certain that the extra increase of the nonlinear lift results from these vortices. This result can be practically applied to the planform design for unmanned aerial vehicles.

scholarly journals A vortex model for forces and moments on low-aspect-ratio wings in side-slip with experimental validation

2017 ◽  
Vol 473 (2198) ◽  
pp. 20160760 ◽  
Author(s):  
Adam C. DeVoria ◽  
Kamran Mohseni
Keyword(s):  
Aspect Ratio ◽  
Leading Edge ◽  
Streamwise Vorticity ◽  
Slender Body Theory ◽  
Vortex Model ◽  
Low Aspect Ratio ◽  
High Incidence ◽  
Stall Angle ◽  
Lift And Drag ◽  
Body Theory

This paper studies low-aspect-ratio ( ) rectangular wings at high incidence and in side-slip. The main objective is to incorporate the effects of high angle of attack and side-slip into a simplified vortex model for the forces and moments. Experiments are also performed and are used to validate assumptions made in the model. The model asymptotes to the potential flow result of classical aerodynamics for an infinite aspect ratio. The → 0 limit of a rectangular wing is considered with slender body theory, where the side-edge vortices merge into a vortex doublet. Hence, the velocity fields transition from being dominated by a spanwise vorticity monopole ( ≫ 1) to a streamwise vorticity dipole ( ∼ 1). We theoretically derive a spanwise loading distribution that is parabolic instead of elliptic, and this physically represents the additional circulation around the wing that is associated with reattached flow. This is a fundamental feature of wings with a broad-facing leading edge. The experimental measurements of the spanwise circulation closely approximate a parabolic distribution. The vortex model yields very agreeable comparison with direct measurement of the lift and drag, and the roll moment prediction is acceptable for ≤ 1 prior to the roll stall angle and up to side-slip angles of 20°.

Experimental Aerodynamic Characteristics of a Compound Wing in Ground Effect

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Saeed Jamei ◽  
Adi Maimun Abdul Malek ◽  
Shuhaimi Mansor ◽  
Nor Azwadi Che Sidik ◽  
Agoes Priyanto
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Center Of Pressure ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Ground Effect ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Ground Clearance

Wing configuration is a parameter that affects the performance of wing-in-ground effect (WIG) craft. In this study, the aerodynamic characteristics of a new compound wing were investigated during ground effect. The compound wing was divided into three parts with a rectangular wing in the middle and two reverse taper wings with anhedral angle at the sides. The sectional profile of the wing model is NACA6409. The experiments on the compound wing and the rectangular wing were carried to examine different ground clearances, angles of attack, and Reynolds numbers. The aerodynamic coefficients of the compound wing were compared with those of the rectangular wing, which had an acceptable increase in its lift coefficient at small ground clearances, and its drag coefficient decreased compared to rectangular wing at a wide range of ground clearances, angles of attack, and Reynolds numbers. Furthermore, the lift to drag ratio of the compound wing improved considerably at small ground clearances. However, this improvement decreased at higher ground clearance. The drag polar of the compound wing showed the increment of lift coefficient versus drag coefficient was higher especially at small ground clearances. The Reynolds number had a gradual effect on lift and drag coefficients and also lift to drag of both wings. Generally, the nose down pitching moment of the compound wing was found smaller, but it was greater at high angle of attack and Reynolds number for all ground clearance. The center of pressure was closer to the leading edge of the wing in contrast to the rectangular wing. However, the center of pressure of the compound wing was later to the leading edge at high ground clearance, angle of attack, and Reynolds number.

scholarly journals Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio

2015 ◽  
Vol 12 (105) ◽  
pp. 20150051 ◽  
Author(s):  
Jan W. Kruyt ◽  
GertJan F. van Heijst ◽  
Douglas L. Altshuler ◽  
David Lentink
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Angle Of Attack ◽  
Radial Distance ◽  
Leading Edge ◽  
High Angle ◽  
High Angle Of Attack ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Low Aspect Ratio Wings

Airplanes and helicopters use high aspect ratio wings to reduce the power required to fly, but must operate at low angle of attack to prevent flow separation and stall. Animals capable of slow sustained flight, such as hummingbirds, have low aspect ratio wings and flap their wings at high angle of attack without stalling. Instead, they generate an attached vortex along the leading edge of the wing that elevates lift. Previous studies have demonstrated that this vortex and high lift can be reproduced by revolving the animal wing at the same angle of attack. How do flapping and revolving animal wings delay stall and reduce power? It has been hypothesized that stall delay derives from having a short radial distance between the shoulder joint and wing tip, measured in chord lengths. This non-dimensional measure of wing length represents the relative magnitude of inertial forces versus rotational accelerations operating in the boundary layer of revolving and flapping wings. Here we show for a suite of aspect ratios, which represent both animal and aircraft wings, that the attachment of the leading edge vortex on a revolving wing is determined by wing aspect ratio, defined with respect to the centre of revolution. At high angle of attack, the vortex remains attached when the local radius is shorter than four chord lengths and separates outboard on higher aspect ratio wings. This radial stall limit explains why revolving high aspect ratio wings (of helicopters) require less power compared with low aspect ratio wings (of hummingbirds) at low angle of attack and vice versa at high angle of attack.

Cross-Wind Influence on Low Aspect Ratio Wings at Low Reynolds Numbers

2013 ◽  
Author(s):  
Amir Karimi Noughabi ◽  
Mehran Tadjfar
Keyword(s):  
Aspect Ratio ◽  
Numerical Study ◽  
Three Dimensional ◽  
Micro Air Vehicles ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Lift And Drag ◽  
Lift And Drag Coefficient

The aerodynamics of the low aspect ratio (LAR) wings is of outmost importance in the performance of the fixed-wing micro air vehicles (MAVs). The flow around these wings is widely influenced by three dimensional (3D) phenomena: including wing-tip vortices, formation of laminar bubble, flow separation and reattachment, laminar to turbulent transition or any combination of these phenomena. All the recent studies consider the aerodynamic characteristics of the LAR wings under the effect of the direct wind. Here we focus on the numerical study of the influence of cross-wind on flow over the inverse Zimmerman wings with the aspect ratios (AR) between 1 and 2 at Reynolds numbers between 6×104 and 105. We have considered cross-wind’s angles from 0° to 40° and angle of attack from 0° to 12°. The results show that lift and drag coefficient generally decrease when the angle of the cross-wind is increased.

scholarly journals Three-dimensional flows around low-aspect-ratio flat-plate wings at low Reynolds numbers

2009 ◽  
Vol 623 ◽  
pp. 187-207 ◽  
Author(s):  
KUNIHIKO TAIRA ◽  
TIM COLONIUS
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Vortex Dynamics ◽  
Large Time ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Tip Vortices ◽  
Wake Vortices ◽  
Low Aspect Ratio

Three-dimensional flows over impulsively translated low-aspect-ratio flat plates are investigated for Reynolds numbers of 300 and 500, with a focus on the unsteady vortex dynamics at post-stall angles of attack. Numerical simulations, validated by an oil tow-tank experiment, are performed to study the influence of aspect ratio, angle of attack and planform geometry on the wake vortices and the resulting forces on the plate. Immediately following the impulsive start, the separated flows create wake vortices that share the same topology for all aspect ratios. At large time, the tip vortices significantly influence the vortex dynamics and the corresponding forces on the wings. Depending on the aspect ratio, angle of attack and Reynolds number, the flow at large time reaches a stable steady state, a periodic cycle or aperiodic shedding. For cases of high angles of attack, an asymmetric wake develops in the spanwise direction at large time. The present results are compared to higher Reynolds number flows. Some non-rectangular planforms are also considered to examine the difference in the wakes and forces. After the impulsive start, the time at which maximum lift occurs is fairly constant for a wide range of flow conditions during the initial transient. Due to the influence of the tip vortices, the three-dimensional dynamics of the wake vortices are found to be quite different from the two-dimensional von Kármán vortex street in terms of stability and shedding frequency.

Thickness Effect on Low-Aspect-Ratio Wing Aerodynamic Characteristics at a Low Reynolds Number

2008 ◽  
Vol 24 (3) ◽  
pp. 223-228 ◽  
Author(s):  
F. B. Hsiao ◽  
C. Y. Lin ◽  
Y. C. Liu ◽  
D. B. Wang ◽  
C. C. Hsu ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Low Reynolds Number ◽  
Aerodynamic Characteristics ◽  
Thickness Effect ◽  
Tip Vortices ◽  
Low Aspect Ratio ◽  
Aerodynamic Properties ◽  
Low Reynolds ◽  
Wing Tips

AbstractThis paper presents the study of aerodynamic performance about low-aspect-ratio wings at a low Reynolds number in wind tunnel testing. The aerodynamic properties, including lift, total drag, lift-to-drag ratio and induced drag were measured and analyzed for detailed investigations. Two forms of nonlinear equations of lift curves were reported for comparison. The effect of airfoil thickness was found to be significant on aerodynamic characteristics for all wings tested. The lift due to tip vortices was prominent for wings of AR =1.0 and their stall angles were all larger than 20°, which was mainly augmented by tip vortices shed from the wing tips.

Perspective: Unsteady Wing Theory—The Ka´rma´n/Sears Legacy

1993 ◽  
Vol 115 (4) ◽  
pp. 548-560 ◽  
Author(s):  
J. E. McCune ◽  
T. S. Tavares
Keyword(s):  
Aspect Ratio ◽  
Small Amplitude ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Unsteady Motion ◽  
Low Aspect Ratio ◽  
Key Concepts ◽  
Edge Separation ◽  
Point Of Departure ◽  
Large Amplitude Motion

The aerodynamic analysis of wings and their vortex wakes is discussed from a perspective of its relation to the 1938 work of Ka´rma´n and Sears. The key concepts from this early paper on the analysis of airfoils in small amplitude unsteady motion are reviewed. These concepts are then used as a point of departure for developing techniques for calculating and interpreting the aerodynamic characteristics of both airfoils in large amplitude motion with deforming vortex wakes, and maneuvering low-aspect-ratio wings with leading-edge separation. Calculated examples are presented for this extended set of applications, and are compared to related analyses and experiments.

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